Multilayer plastic containers and preforms typically include one or more layers of plastic resin such as polyethylene terephthalate (PET) alternating with one or more layers of barrier resin such as nylon or ethylene vinyl alcohol (EVOH) to resist transmission of gas, water vapor and/or flavorants, including odorants and essential oils, through the container wall. An important property of containers of this type is interlaminar adhesion to resist delamination between or among the various layers during filling and handling of the containers by the container manufacturer and the product packager, and during use of the container by the consumer. Various techniques have been proposed for increasing interlaminar adhesion, which generally result in a decrease in barrier properties, an increase in manufacturing cost and/or an increase in other undesirable container properties such as haze in the container wall. It is therefore a general object of the present invention to provide a multilayer container, a container preform and a method of manufacture having improved adhesion characteristics between the layers of the container (and preform) wall without significantly affecting container cost or other parameters of manufacture.
A plastic container in accordance with one presently preferred aspect of the invention includes a multilayer wall having at least one layer of polyester resin, at least one layer of barrier resin, and an adhesion-promoting material blended with the barrier resin and/or the polyester resin to promote bonding between the barrier and polyester layers. In the preferred embodiments of the invention, the adhesion-promoting material is blended with the barrier resin. The adhesion-promoting material includes an organometallic coupling agent based upon titanium, zirconium or aluminum. The organometallic coupling agent preferably has an amino end group with an affinity for the carboxylic end group of the polyester, and preferably is selected from the group consisting of neopentyl(diallyl)oxy, tri(N-ethylenediamino) ethyl titanate, zirconate and aluminate. Coupling agents based upon titanium and zirconium are particularly preferred for containers having a clear (non-colored) wall.
The polyester resin preferably is selected from the group consisting of PET, polyethylene naphthalate (PEN), blends and copolymers of PET and PEN, and process regrind that consists essentially of PET, PEN, or blends or copolymers of PET and PEN. The barrier resin preferably is selected from the group consisting of EVOH, nylon, acrylonitrile copolymers, blends of EVOH and nylon, nanocomposites of EVOH or nylon and clay, blends of EVOH and an ionomer, acrylonitrile, cyclic olefin copolymers, polyglycolic acid (PGA), and blends thereof. EVOH and meta-xylylenediamine (MXD) nylon are particularly preferred. Active oxygen absorbing barrier resins also may be employed in combination with or in place of the listed passive barrier resins.
Other aspects of the invention include a plastic container preform, methods of making a plastic container and a preform, a barrier resin blend, a method of processing a barrier resin and a multilayer article in accordance with the invention.